Association of Training in Basic Life Support with the Evolution of Cardiopulmonary Resuscitation Performed by Firefighters

Introduction This study aimed to compare the results of professional technical and anthropometric anamnesis data with the transmission of external chest compressions performed by military firefighters at different execution times. Objective The objective was to evaluate the performance and perceived effort of the sequence of external chest compressions performed in two minutes, as well as the evolution of the technique over time. Materials and Methods This was a descriptive, correlational study involving adult firefighters who were members of a specific firefighter group, comprising a population of 105 individuals with a voluntary sample of 44 participants. The study used a Bayesian statistical approach to provide probabilistic expressions. Results The participants had an average work experience of 17 years, an average age of 38.6 years, an average weight of 81.48 kilograms, an average height of 176 centimeters, and an average of 2.5 qualifications. The results indicated that the firefighters performed external chest compressions with excellent technique and a moderate level of perceived effort in a two-minute evaluation. The evaluation of the evolution of the technique over time showed that the participants were able to maintain high-quality compressions for an average of 6 minutes, with a maximum of 20 uninterrupted minutes. Conclusion The study underscores the critical role of professional firefighters in performing and maintaining high-quality external chest compressions, which has the potential to reduce morbidity and mortality in cases of cardiorespiratory arrest.


Introduction
Te performance of cardiopulmonary resuscitation (CPR) in pre-hospital care settings is crucial, particularly when carried out by well-trained teams in large networks. In Brazil, the Fire Department plays a vital role in these situations as they frequently respond to out-of-hospital cardiorespiratory arrests (CRA) and perform CPR using motorcycles and rescue vehicles. CPR is the primary intervention for CRA, as it helps to maintain blood circulation, and its prompt implementation is one of the key factors in the success of resuscitation for individuals who experience CRA outside of a hospital setting, thereby signifcantly increasing their chances of survival [1][2][3][4][5]. Efective CPR requires external chest compressions (ETCs) at a rate of 100 to 120 movements per minute and a depth of 5 to 6 centimeters in adults, emphasizing the importance of good-quality CPR and its timely implementation [1]. However, performing high-quality CPR can lead to rescuer fatigue [6,7] causing a decrease in the quality of ETCs during CPR after two minutes [8,9], which is why it is recommended that rescuers be replaced every two minutes [1].
Te Ministry of Health's Ordinance 2048 (2002) establishes and regulates Pre-Hospital Care (APH) services in Brazil. In the State of São Paulo, the Fire Department, as part of the Military Police, is responsible for pre-hospital APH care. Teir goal is to provide prompt and appropriate care, stabilize the patient's vital signs, reduce morbidity and mortality, and quickly transport the patient to adequate medical care.
To achieve these goals, it is essential to work in large networks and with well-trained teams. In Brazil, the Fire Department plays a crucial role in these services, providing daily support to health units with motorcycles and rescue vehicles. Tey are usually the frst professionals to face outof-hospital CPA and are capable of performing cardiopulmonary resuscitation (CPR).
In the ambulance, the rescue team of the Fire Department comprises three rescuers who provide hands-on assistance in any occurrence. Tey are not authorized to administer medication or perform invasive procedures. Te Fire Department's response time, from receiving the call to the arrival of the vehicles to attend to the occurrence, is approximately 10 minutes in Brazil.
Basic Life Support (BLS) training is critical for providing care to patients in CRA in out-of-hospital environments [1], but even with training, people still sometimes fail to perform chest compressions during [10]. Hence, the ongoing training of rescuers is crucial for providing life support in cardiovascular emergencies [11][12][13]. Te monitoring of ETCs during training and further scientifc research into the effectiveness of these procedures is a critical need in the feld of CPR [14]. Te present study aimed to investigate the relationship between BLS training and the efectiveness of CPR performed by frefghters and to examine the association between the amount of training received and the time of voluntary interruption due to rescuer fatigue during the performance of ETCs. Te hypothesis of the study was that frefghters with more BLS training would exhibit higher efectiveness in CPR, with a focus on ETCs, and would have a longer duration of efective CPR performance before voluntarily interrupting due to exhaustion.

Materials and Methods
Te target population of this study was adult frefghters working at the 9th Group of Firefghters in the city of Ribeirão Preto, São Paulo. Te sample was voluntary and consisted of 105 frefghters, but only 44 of them who fully participated in all stages of the study were included. Te inclusion criteria were being a frefghter working in Ribeirão Preto and exclusion criteria was being on sick leave, leave, or vacation during the data collection period. Te sample size was calculated using G * Power software (version 3.1, University of Düsseldorf ) based on a predicted efect size of 0.4 and a desired power of 80% at an alpha level of 0.05 [15]. Te study was approved by the Ethics and Research Committee and registered at Plataforma Brasil with CAAE 10431719.9.0000.5393. Te data collection took place from January to November 2020, including the interruption of activities due to the Covid-19 pandemic.
Tis study is a descriptive and correlational investigation comparing the results of professional technical anamnesis with the performance of CPR, with a focus on chest compressions, among military frefghters. Te study was conducted in four stages at the Command Headquarters of the 9th Group of Firefghters in Ribeirão Preto, São Paulo. Te execution time of CPR was two minutes or until voluntary exhaustion ( Figure 1).
Te frst stage-invitation and participants characterization: Participants were contacted personally in the fve barracks of the 9th Group of Firefghters located in Ribeirão Preto, São Paulo. Te study was introduced to the participants, and those who consented signed an Informed Consent Form (ICF) and completed the technical-professional anamnesis form. Te technicalprofessional anamnesis was conducted through a questionnaire designed by the researchers as a control mechanism and for characterizing the participants. Te data collected from the questionnaire and throughout the study were only used for the purposes explicitly stated in the ICF. Te questionnaire was developed by the researcher and included information such as the participant's name, gender, date of birth, marital status, academic background, date of admission to the corporation, frefghter specialization courses, and physical activity practices. Te second stage-theoretical-practical training: Te volunteers underwent theoretical and practical training, which lasted approximately 15 minutes in the theoretical component. During this time, they received an update on CPR/CPR and CTEs in accordance with the guidelines recommended by the American Heart Association [1] for Basic Life Support (BLS). Ten, they underwent two practical CPR training sessions, with an emphasis on CTEs, using a Laerdal Resusci Anne Wireless SkillReporter manikin. Tis manikin provides real-time feedback to the participant during the training, allowing for high-performance practical skills training for healthcare professionals and frst responders. Te manikin ofers precise and profcient CPR training, enabling the use of protocols, equipment, and techniques used in real-life situations. To ensure standardization and proximity to real-life scenarios, the participants were dressed in the operational work clothes of frefghters and wore gloves for procedures and a surgical mask. At the end of the CPR simulations, a feedback report was generated by the manikin and entered into a Microsoft Excel database for statistical analysis. In the frst period of practical training, participants performed two minutes of CTEs with feedback, along with verbal encouragement from the evaluators. In the second training period, after approximately 30 minutes of rest, the volunteers performed the CTEs again, until they voluntarily stopped due to exhaustion, with feedback on the efectiveness of the CTEs (frequency and depth) and verbal encouragement from the evaluators. Te third stage-evaluation of the efectiveness of CPR with a focus on chest compression techniques: After a minimum interval of 48 hours and a maximum of one week, the volunteers performed chest compression techniques on the Laerdal Resusci Anne Wireless SkillReporter manikin, lasting for two minutes, without receiving feedback from the manikin or evaluators. In this stage, the efectiveness of the chest compressions performed by the participants was assessed. Te participants' initial and fnal heart rates were recorded before and after each test, respectively. Te fourth stage-CTE efectiveness test with emphasis on CTEs: After a minimum period of 48 hours and a maximum of one week, participants performed CTEs on a manikin, continuing until voluntary exhaustion, with no feedback from either the manikin or evaluators. At this stage, the efectiveness of the CTEs performed by the participants until voluntary exhaustion was evaluated. Te participant's initial and fnal heart rate was checked at the beginning and end of each test. Statistical analyses were performed using JASP software (Amsterdam, Netherlands) version 0.12.2. A Bayesian statistical approach was employed to provide probabilistic assertions, as it ofers a valuable alternative to interpreting the relative support of a null hypothesis against an alternative hypothesis [16,17]. Te normality of data distribution was confrmed using Q-Q plots, and data are reported as mean ± standard deviation (SD). Te Bayes Factor (BF10) was calculated for all variables using the "uninformative" hypothesis predefned by JASP (Cauchy, 0.707). Evidence for the alternative hypothesis (H1) was established as BF10 > 3 and evidence for the null hypothesis (H0) as BF10 < 1/3. BF calculates the probability that the null (H0) or alternative (H1) hypothesis is true given the current data. In case of a signifcant H1-favorable Bayes Factor (BF10), a post hoc analysis was performed [18]. BF10 was reported to indicate the strength of evidence for each analysis (within and between) and interpreted as anecdotal (BF10 � 1-3), moderate (BF10 � 3-10), strong (BF10 � 10-30), very strong (BF10 � 30-100) when favoring the alternative hypothesis; or anecdotal (BF10 � 1-0.33), moderate (BF10 � 0.33-0.01), strong (BF10 � 0.01-0.03), very strong (BF10 � 0.03-0.01), and extreme (BF10 < 0.01) when favoring the null hypothesis [19].

Results
In Table 1, the characterization of the participants is presented regarding the variables obtained in the technicalprofessional anamnesis. Of the 44 (100%) professional frefghters who made up the sample in this study, all were male. Te mean of the subjective scale of perceived exertion (3.00), during the CTEs, was considered moderate ( Table 2). Table 3, presents the correlation between the variables referring to the characterization of the professional frefghter and the efectiveness of the CTEs in the two-minute test. Te analysis regarding the relationship between the presence of training/specialization courses for frefghters and the efectiveness of CTEs performed within two minutes showed that there is a moderate correlation between the number of courses taken and the reduction of subjective fatigue during the two-minute efort. Specifcally, the more training sessions taken, the greater the positive impact on reducing the feeling of fatigue during CTEs. Table 4 presents the results of the assessment of the efectiveness of CPR via the voluntary interruption test (time to exhaustion). Te assessment of the efectiveness of the CTEs based on the time to exhaustion revealed that, primarily, the maximum time that participants were able to perform CTEs with quality and efectiveness was 20 uninterrupted minutes. Only one participant was unable to reach the minimum required time of two minutes. Although the participants rated the difculty level during the evaluation as 4.80, it was considered relatively manageable. Te correlation between the characteristics of professional frefghters and the efectiveness of the CTEs as determined by the time to exhaustion test is presented in Table 5.
Te analysis of the relationship between the efectiveness of CTEs until exhaustion and variables pertaining to the characterization of participants in the present study revealed a moderate negative correlation between the body weight of the frefghters and the ability to maintain proper hand placement on the victim's chest during compressions. In other words, a greater body weight among professionals was associated with increased difculty in maintaining proper hand placement during the CTEs.

Discussion
Te objective of this study was to examine the relationship between basic life support training and the efectiveness of cardiopulmonary resuscitation (CPR) performed by frefghters and to assess the correlation between the amount of  Emergency Medicine International training received and the time of voluntary interruption due to exhaustion during CPR. Despite the signifcance of CPR in an out-of-hospital environment and the crucial role played by frefghters in performing CPR [20], studies on the relationship between physical ftness, body composition, and the efectiveness of CPR typically do not consider frefghters as a distinct population [21], highlighting the need and importance of addressing this demographic in this context [9,12].
In line with this objective, this study recruited 44 male professional frefghters as participants. Most of them were experienced in their feld, adults, and had an average body weight and height that is typical for their profession [22,23]. Other studies that have studied frefghters as a population have similar sample characteristics and inclusion criteria as this research [22,[24][25][26].
Te average number of training courses and specializations taken by the participants was 2.5, with 10 professionals having not taken any specialization courses. Te teaching and learning processes adopted for frefghter training are of interest to the felds of health, education, and resuscitation, as developing these skills is essential for the profession [27]. A moderate correlation was found in the study between the number of courses taken and the decrease in feelings of subjective fatigue during two-minute CPR eforts. Tis indicates that greater technical-scientifc preparation results in less difculty and fatigue perceived during CPR.
Ferreira Junior et al. found a correlation between CPR knowledge and age among frefghters, with those under 35 having gaps in CPR knowledge due to a lack of specialized training and a lack of variety of training necessary for developing knowledge, skills, and attitudes for daily practice [28]. Tis can negatively impact the quality of CPR and increase fatigue during the procedure. Adopting simulator mannequins is becoming increasingly popular for frefghter training as they enable the development of psychomotor skills necessary for professional practice [27].
Regardless of the number of events in which a soldier has participated throughout his career, no two situations will ever be identical. Te variables involved, such as the characters, psychological and material conditions, external interferences, and risks to be overcome, all difer. To address this variability of events, technical-scientifc preparation is necessary, which can be enhanced through courses and training conducted during professional experience [29].
Te efectiveness of cardiopulmonary resuscitation (CPR) procedures (CTEs) was found to be of interest, a priori, in a time frame of two minutes. Firefghters were observed to perform the procedure well within this time frame, with an average perceived exertion score classifed as moderate. However, this fnding can negatively impact the quality of the CTE and increase fatigue during the procedure [28]. In another perspective, a cross-sectional study with 63 university students trained in CPR analyzed the relationship between muscle strength and CTEs and concluded that the ability to provide efective CTEs is infuenced by the rescuer's muscle strength, with individuals of lower weight having lower results, particularly in terms of correct compression depth, compared to those with normal weight and those with overweight/obesity [30].
A similar cross-sectional study of 48 trained rescuers, aged between 26 and 46 years, aimed to perform CTEs on a simulator dummy until they reached the maximum reported level of fatigue. Te average duration of the CTEs was 3.28 minutes with a standard deviation of 1.04 minutes, with better times being achieved by those with higher levels of physical activity. Tis study concluded that the greater  the physical preparation, the lower the level of fatigue and the greater the duration of the CTEs [9]. Maintaining a CTE time of approximately 5 minutes and reaching 20 uninterrupted minutes with a level of fatigue classifed as "a little difcult" are important fndings of the present study, as the literature typically describes rescuer fatigue within the frst minute of CTE [9,31,32]. It is possible that a rescuer who is capable of performing a high-quality CTE for a longer duration has a high level of physical training, which positively impacts the reduction of fatigue and maintains their muscular, physical, and cardiorespiratory capacity, ensuring their ability to efectively perform the CTE [33].
Te Voluntary Interruption Test revealed that a professional's body weight afects their ability to maintain hand contact with the thoracic region during compressions. A cross-sectional study involving 63 university students previously trained in CPR found that the rescuer's muscle strength impacts their ability to perform efective compressions. Tis study concluded that individuals with low weight had lower results in terms of compression depth, compared to those with normal weight and those with overweight/obesity [31]. Tis suggests that variations in weight, whether low or high, can negatively impact the quality of compressions. Further studies are necessary to confrm these fndings [34,35].

Emergency Medicine International
Te limitations of this work included the scarcity of literature regarding the relationships between physical ftness, body composition, and the efectiveness of compressions, particularly among professional frefghters. Tis makes it challenging to compare results in diferent scenarios. Nevertheless, this did not hinder the analysis and interpretation of the results.
More research is needed in this area, specifcally welldesigned studies with a high level of evidence, to evaluate the efectiveness of compressions in diferent groups of rescuers with varying body compositions. Tis will contribute greatly to research, teaching, and assistance.

Conclusion
Specifcally, the evaluation of CTE efectiveness, conducted over two minutes, indicated excellent performance by frefghters and a moderate level of perceived efort during compressions. Te voluntary interruption test for exhaustion showed that, on average, the participants were able to perform high-quality compressions for up to 6 minutes, with some reaching as much as 20 uninterrupted minutes. Te subjective perception of fatigue during this test was described as manageable.
Tis study is signifcant because of the crucial role professional frefghters play in performing efective CTEs, which can impact the reduction of morbidity and mortality in CPR cases. Te results of this research have multiple implications, including the development of training and educational strategies tailored to professional frefghters, improvement in the quality of CTEs performed by frefghters, and the potential to replicate these fndings in other professional felds to promote education, research, and assistance in CPR. Tis knowledge can also contribute to the improvement of patient safety and quality of care in CPR, particularly in terms of high-quality compressions. Tis study highlights the importance of a multidisciplinary approach to care, encompassing felds such as nursing, frefghting, and physical education, in the pursuit of life-saving knowledge.

Data Availability
Readers can access the data through the tables and fgures available in the manuscript, and if they want to check in depth, they should contact the authors by e-mail.